The objective of our original grant application was to identify the gene underlying the spontaneous, autosomal, recessive mouse mutation named "chronic proliferative dermatitis" (original mutant locus symbol: cpdm). This was accomplished and identified as Sharpin. The function of the mutated Sharpin gene, responsible for the cpdm phenotype, is poorly understood. Mice carrying spontaneous mutations in Sharpin reveal that it plays a key role in normal development of secondary lymphoid organs and its absence leads to eosinophilia with accumulations of eosinophils and other inflammatory cells in parenchymous organs. These mutant mice develop a severe psoriasiform skin disease characterized by persistent, marked, epidermal hyperplasia, accompanied by apoptotic keratinocytes, accumulation of eosinophils, and concurrent increases in cutaneous mast cells, macrophages, and other inflammatory cells. Inflammatory changes are also evident in other organs including joints, lungs, upper gastrointestinal tract, and liver. Experiments proposed here will define the function of Sharpin and determine how this gene modulates normal immune system development, and controls inflammation in the skin and other organs. We will utilize gene arrays and network analysis software in time course studies to determine the molecular events involved. Crossing a floxed Sharpin transgenic mouse with various promoter-Cre recombinase genetically engineered mice available in our repository will allow us to determine the effects of ubiquitous and organ- or cell-specific inactivation of Sharpin. Cell transfection studies and chlP-on-chip approaches will identify targets allowing us to determine in which gene/protein networks Sharpin functions. These approaches will define the temporal pathogenesis of skin and immune system abnormalities due to inactivation of the Sharpin gene and determine in which molecular pathway(s) this gene functions. The chronic proliferative dermatitis mutant mouse is a valuable tool to define what appears to be a novel disease mechanism for immune system development and psoriasiform dermatitis. Relevance to Public Health: We identified a gene that when mutated, results in severe systemic inflammatory disease that shares pathologic changes with several human diseases. We will define the molecular pathogenesis of the mouse disease. It is likely that a homologous condition exists in humans and knowledge learned from the mouse model will aid in diagnostic test and therapy development.